1. Field of the Invention
The present invention relates to a process for producing biofuels as alternatives or additives to currently used petroleum-based automotive or other vehicular fuels and lubricants by reacting fats and oils such as triglycerides and free fatty acids in a single critical phase to provide increased reaction rates and decrease the loss of catalyst or catalyst activity. The invention includes the transesterification of triglyceride-containing substances and esterification of free fatty acid-containing substances with alcohol to produce alkyl esters of triglycerides, a desirable additive or alternative for petroleum diesel fuel or lubricants.
2. Description of the Prior Art
Significant quantities of esters such as triglycerides and free fatty acids are available from inexpensive feedstocks such as, animal fats, vegetable oils, rendered fats, restaurant grease and waste industrial frying oils. The triglyceride esters can be reacted, or transesterified, with alcohol to produce glycerol and the alkyl esters, and the free fatty acid can be reacted, or esterified, with alcohol or water to produce the alkyl ester. These alkyl esters create desirable additives or alternatives to petroleum diesel fuel as well as other high value end products such as detergent surfactants, herbicides, pesticide diluents, sticking agents, or lubricating additives for hydraulic and transmission fluids to name a few. Consequently, numerous patents exist dealing with processes surrounding transesterification of triglycerides and esterification of free fatty acids with alcohols such as methanol, ethanol or butanol to create the corresponding alkyl esters. U.S. Pat. Nos. 5,713,965 and 5,525,126, incorporated herein by reference, are examples of such processes.
The transesterification or esterification reaction is normally carried out in an excess of the stoichiometric quantity of alcohol and a catalyst, usually a base such as potassium hydroxide although, the reaction can also proceed with an acid catalyst as well. In addition to creation of the alkyl esters, the transesterification reaction also produces glycerol.
Traditionally, triglyceride transesterification requires a multiple step process with one or more batch reactors. Initially, the triglycerides and alcohol form two immiscible liquid phases. As the reaction proceeds, two separate liquid phases form. One contains the newly formed alkyl esters of the triglyceride and the other the glycerol with the excess alcohol, catalyst and feed oil being dispersed into both phases. The reaction time for each step typically is measured in hours and once completed the liquid products must be allowed sufficient time to separate phases before additional processing and separation steps can occur to produce the final products. Excess alcohol must be recycled and the unused catalyst typically must be neutralized.
Even the most efficient of the traditional processes require multiple hours to process each batch of feed. Additionally, significant problems arise in the separation steps. Significant quantities of glycerol left in the alkyl esters diminishes the quality of the diesel fuel and likewise contaminated glycerol also loses much of its value compared to pure uncontaminated glycerol. Traditionally the separation procedures necessary to adequately clean the two product streams produces large quantities of waste water thereby creating additional cost and/or process complexity.